Aerofoil accessories and method for modifying the geometry of a wing element

Abstract

Aerofoil accessories are provided, configured for selective attachment to a wing element, the wing element having an outer facing aerofoil surface and being based on at least one datum aerofoil section. Each accessory provides a modified geometric profile to a datum profile of the at least one aerofoil section when attached to the wing element. The accessories are each configured for having a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element is airborne with the respective accessory attached to the wing element. The modified geometric profile is such as to provide said wing element with the accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent the accessory. A kit is also provided for enhancing performance of a wing element in off-design conditions. A method is also provided for enhancing performance of a wing element in adverse conditions.

The invention claimed is: 
     
       1. An aerofoil-aerofoil accessory assembly, comprising:
 a wing element having an outer facing aerofoil surface and having wing sections in the form of at least one datum aerofoil section defining a datum profile, the wing element including a main primary element and a secondary element separated from said main primary element via a spacing; and 
 an aerofoil suction surface accessory being selectively and reversibly attached to the wing element and configured for providing a modified geometric profile to the at least one datum aerofoil section with respect to the datum profile when said accessory is attached to the wing element, said wing element being designed for aerodynamic flight absent said aerofoil suction surface accessory, said aerofoil suction surface accessory configured for maintaining a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element with said aerofoil suction surface accessory thereon is airborne, said modified geometric profile being such as to provide said wing element with said aerofoil suction surface accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent said aerofoil suction surface accessory, and wherein said aerofoil suction surface accessory provides said modified geometric profile in a manner that is fixed at least during flight, said aerofoil suction surface accessory comprising an outer surface outwardly curving, the outer surface being configured for providing or enhancing mild stall performance, the aerofoil suction surface accessory mounted to a suction surface of an aft section of the main primary element of the wing element. 
 
     
     
       2. The aerofoil-aerofoil accessory assembly according to  claim 1 , wherein said aerofoil suction surface accessory is configured for effectively providing said modified profile with at least a change in a suction surface profile thereof with respect to said datum profile. 
     
     
       3. The aerofoil-aerofoil accessory assembly according to  claim 2 , wherein said outer facing aerofoil surface comprises a local curvature that may increase, or that may remain substantially constant, along the chord in a direction towards a trailing edge of the primary element when said aerofoil suction surface accessory is attached to the wing element. 
     
     
       4. A method for modifying a geometry of a wing element with an aerofoil suction surface accessory, the method comprising:
 providing the wing element having an outer facing aerofoil surface and having wing sections in the form of at least one datum aerofoil section defining a datum profile, the wing element including a main primary element and a secondary element separated from said main primary element via a spacing, the wing element being designed for aerodynamic flight absent said aerofoil suction surface accessory; and 
 attaching the aerofoil suction surface accessory to a suction surface of an aft section of the main primary element of the wing element, said aerofoil suction surface accessory being selectively and reversibly attached to the wing element and configured for providing a modified geometric profile to the at least one datum aerofoil section with respect to the datum profile when said aerofoil suction surface accessory is attached to the wing element, said aerofoil suction surface accessory configured for maintaining a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element with said aerofoil suction surface accessory thereon is airborne, said modified geometric profile being such as to provide said wing element with said aerofoil suction surface accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent said aerofoil suction surface accessory, and wherein said aerofoil suction surface accessory provides said modified geometric profile in a manner that is fixed at least during flight, said aerofoil suction surface accessory including an outer surface outwardly curving, the outer surface being configured for providing or enhancing mild stall performance. 
 
     
     
       5. The method according to  claim 4 , wherein said aerofoil suction surface accessory is attached to the wing element when it is desired to provide a desired high lift, mild stall performance to the wing element. 
     
     
       6. An aerofoil-aerofoil accessory assembly, comprising:
 a wing element having an outer facing aerofoil surface and having wing sections in the form of at least one datum aerofoil section defining a datum profile, the wing element including a main primary element and a secondary element separated from said main primary element via a spacing; and 
 an aerofoil pressure surface accessory being selectively and reversibly attached to the wing element and configured for providing a modified geometric profile to the at least one datum aerofoil section with respect to the datum profile when said accessory is attached to the wing element, the wing element being designed for aerodynamic flight absent said aerofoil pressure surface accessory, said aerofoil pressure surface accessory configured for maintaining a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element with said aerofoil pressure surface accessory thereon is airborne, said modified geometric profile being such as to provide said wing element with said aerofoil pressure surface accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent said accessory, and wherein said aerofoil pressure surface accessory provides said modified geometric profile in a manner that is fixed at least during flight, said aerofoil pressure surface accessory attached to a pressure surface of the main primary element of the aerofoil, and configured for minimizing or avoiding accretion of contaminant on said secondary element when subjected to an airflow comprising said contaminant, the contaminant being in the form of particulate matter flowing in a downstream direction with respect to a leading edge of said main primary element; and 
 wherein said aerofoil pressure surface accessory includes a profile configured to ensure that at least some streamlines proximate to said pressure surface of said main primary element follow a path including over a suction surface of said secondary element spaced from the main primary element via said gap, while concurrently providing a trajectory to particulate matter flowing in said at least some streamlines proximate to said pressure surface of said main primary element to cause said particulate matter to overshoot said gap. 
 
     
     
       7. The aerofoil-aerofoil accessory assembly according to  claim 6 , wherein said aerofoil pressure surface accessory is configured for effectively providing said modified profile with at least a change in a pressure surface profile thereof with respect to said datum profile. 
     
     
       8. The aerofoil-aerofoil accessory assembly according to  claim 7 , wherein said aerofoil pressure surface accessory is configured for preventing or minimizing accretion of contaminants on said secondary element when attached to said primary element. 
     
     
       9. The aerofoil-aerofoil accessory assembly according to  claim 8 , wherein said outer facing aerofoil surface comprises an accessory profile configured for minimizing or preventing flow into said gap of said contaminants that may be flowing along or proximate to a boundary layer over said pressure surface. 
     
     
       10. The aerofoil-aerofoil accessory assembly according to  claim 8 , wherein said accessory surface profile extends outwardly along at least a portion of the chord of said primary aerofoil element with respect to the original pressure surface profile of the aerofoil. 
     
     
       11. The aerofoil-aerofoil accessory assembly according to  claim 8 , wherein said accessory surface profile comprises a convex curvature between a forward edge and an aft edge of the accessory. 
     
     
       12. The aerofoil-aerofoil accessory assembly according to  claim 8 , wherein said pressure surface profile comprises an upstream concave portion configured for imparting a centrifugal force component to said particulate matter, and a downstream convex portion joined thereto at an inflexion point. 
     
     
       13. A method for modifying a geometry of a wing element with an aerofoil pressure surface accessory, the method comprising:
 providing the wing element having an outer facing aerofoil surface and having wing sections in the form of at least one datum aerofoil section defining a datum profile, the wing element including a main primary element and a secondary element separated from said main primary element via a spacing, the wing element being designed for aerodynamic flight absent said accessory; and 
 attaching the aerofoil pressure surface accessory to a pressure surface of the main primary element of the wing element, said aerofoil pressure surface accessory being selectively and reversibly attached to the wing element and configured for providing a modified geometric profile to the at least one datum aerofoil section with respect to the datum profile when said aerofoil pressure surface accessory is attached to the wing element, said aerofoil pressure surface accessory configured for maintaining a substantially fixed geometric profile with respect to the at least one datum aerofoil section at least whenever said wing element with said aerofoil pressure surface accessory thereon is airborne, said modified geometric profile being such as to provide said wing element with said aerofoil pressure surface accessory attached thereto with a desired change in performance relative to a datum performance provided by the wing element absent said aerofoil pressure surface accessory, and wherein said aerofoil pressure surface accessory provides said modified geometric profile in a manner that is fixed at least during flight, said aerofoil pressure surface accessory configured for minimizing or avoiding accretion of contaminant on said secondary element when subjected to an airflow comprising said contaminant, wherein the contaminant is in the form of particulate matter flowing in a downstream direction with respect to a leading edge of said main primary element; and 
 wherein said pressure surface accessory includes a profile configured to ensure that at least some streamlines proximate to said pressure surface of said main primary element follow a path including over a suction surface of said secondary element spaced from the main primary element via said gap, while concurrently providing a trajectory to particulate matter flowing in said at least some streamlines proximate to said pressure surface of said main primary element to cause said particulate matter to overshoot said gap. 
 
     
     
       14. The method according to  claim 13 , wherein said pressure surface accessory is attached to the wing element when it is desired to minimize or prevent accretion of contaminants on the second element of said wing element. 
     
     
       15. A method of operating an air vehicle, comprising
 providing an air vehicle having fixed-wings, each said fixed wing including a wing leading edge; 
 providing a leading edge slot accessory for each said fixed wing, each said leading edge slot accessory being configured for being selectively and reversibly affixed to each said wing leading edge to provide a leading edge slot between the leading edge slot accessory and the wing leading edge, said fixed wings being designed for providing aerodynamic flight absent said leading edge slot accessory; 
 selectively affixing the leading edge slot accessory to each of the fixed wings to provide increased maximum lift performance of the thereby modified fixed wings to enable the air vehicle to take-off with a heavy payload for a predetermined mission under predetermined conditions as compared with a datum maximum lift performance obtained with said fixed wing absent said leading edge slot accessory, wherein under said predetermined conditions the corresponding said datum maximum lift performance of said fixed wings absent said leading edge slot accessory is insufficient for enabling take-off of the air vehicle with said heavy payload; and 
 flying said air vehicle in said predetermined mission. 
 
     
     
       16. The method according to  claim 15 , further comprising removing the leading edge slot accessory from each of the fixed wings after termination of said predetermined mission. 
     
     
       17. The method according to  claim 15 , wherein said fixed wing comprises a wing element, the wing element comprising a primary element including at least a part of the wing leading edge, and a secondary element separated from the primary element via a spacing. 
     
     
       18. The method according to  claim 15 , wherein said leading edge slot accessory maintains a substantially fixed geometric profile with respect to the at least one datum aerofoil section of the fixed wing at least whenever said fixed wing with said leading edge slot accessory affixed thereon is airborne.